Entire screen flickers black if one adds QOpenGLWidget to full-screen QMainWindow

Flickering happens if I call showFullScreen() on QMainWindow, either before or after adding child opengl widget.
If multiple screens are used, all of them flicker. But if window is moved to second (non-main) screen, there is no flickering.
If I set other screen as main in Windows configuration, flickering happens on new main screen.

I attached a minimal example project.
This issue can be also reproduced in 2dpainting example, if you add setFullScreen() call to Window class ctor.

Edit: corrected description.